1. Field of the Invention
The present invention relates to a cutting insert and an indexable face mill on which such cutting inserts are mounted.
2. Description of the Related Art
Cutting inserts have been proposed that are available both for a case wherein, when the cutting inserts are mounted on a face mill, they are to be fed to the right of the inserts, as viewed from the front in the rotational direction of the tool (hereinafter, this is referred to as a right hand cut), and for a case wherein they are to be fed to the left of the inserts, as viewed from the front in the rotational direction of the tool (hereinafter, this is referred to as a left hand cut).
A cutting insert disclosed in Japanese Patent Laid-Open No. 2006-224278 has a nearly polygonal shape, whereon paired minor cutting edges are provided for the individual corners, and are extended along the side ridges, while being inclined inwardly from the side ridges, and whereon clearance parts are formed between the individual minor cutting edge pairs, at a location inward from the insert relative to intersecting points of lines extended from the paired minor cutting edges. The clearance parts each include a flat portion and a V-groove or a round groove, formed between the minor cutting edge pair.
According to the Japanese Patent Laid-Open No. 2006-224278, the clearance parts are positioned between the minor cutting edge pairs, at the interior of the cutting insert, relative to the intersecting points of lines extended from the paired minor cutting edges. Therefore, in a case wherein this insert is employed for both a right hand cut and a left hand cut, when one of the paired minor cutting edges has been worn out by cutting, an increase in the wear can be prevented by the presence of the clearance part, and wear of the other minor cutting edge can be avoided.
However, since the cutting insert described in Japanese Patent Laid-Open No. 2006-224278 includes the clearance parts positioned between the minor cutting edge pairs, that are formed at the interior of the insert, relative to the intersecting points of the lines extended from the paired minor cutting edges, the strength of the portions of the individual minor cutting edges adjacent to the clearance parts is reduced. Therefore, chipping or fracturing of the minor cutting edges may occur, and the finished surface roughness may be lowered. Furthermore, during the face milling process, when the cutting insert is positioned to the front of the center of the face mill in the feeding direction F, the cutting of a workpiece is to be performed, while when the cutting insert is positioned to the rear of the center in the feeding direction F, the cutting insert does not have an apparent contact with the workpiece. However, in actuality, since the inclination of the face mill body itself caused by cutting resistance or the main spindle of a machining tool, etc., are present a phenomenon has occurred that cutting inserts 101, which are located to the rear of the center of the face mill 100 in the feeding direction F, contact the work surface of the workpiece and perform micro-cutting on the work surface (see FIG. 8). During this micro-cutting, the portions where the minor cutting edges and the clearance parts are adjacent to each other contact the workpiece first, and cut the work surface. Since as described above the strength of the adjacent portions is lowered, the load due to micro-cutting is easily imposed on these portions, and chipping tends to occur. Therefore, there is a probability that the chipped minor cutting edges and the clearance parts will contact the work surface and degrade the surface roughness of the work surface.